In recent years, numerous proposals have been made for use of the clean energy hydrogen as a source of energy.
To produce hydrogen, steam reformation using a hydrocarbon fuel has been the general practice. In recent years, consideration has been given to obtaining hydrogen from water by water splitting, in particular the water splitting using solar energy. In particular, when generating hydrogen by splitting water, photocatalytic decomposition of water using solar energy is gathering attention in the point of enabling the utilization of the inexhaustible solar energy.
Regarding the separation of hydrogen from the mixture of hydrogen, oxygen, and water obtained by water splitting, Japanese Unexamined Patent Publication (Kokai) No. 2004-35356 and Japanese Unexamined Patent Publication (Kokai) No. 2004-292284 propose using a hydrogen separating membrane selectively allowing the passage of only hydrogen. Note that, Japanese Unexamined Patent Publication (Kokai) No. 2008-207969 proposes using a hydrogen separating membrane for separation of hydrogen from a mixed gas obtained by steam reformation using a hydrocarbon fuel.